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Phytophthora capsici is a highly destructive pathogen of pepper. To examine whether proline modifies the levels of plant defense compounds produced in response to P. capsici-induced stress, pepper seedlings were infected with P. capsici-22 in the presence of proline (1 mM, 10 mM) or in its absence. Proline was sprayed on the leaves of CM-334 and Kekova pepper cultivars prior to inoculation. CM-334 was more resistant to P. capsici-22, while the Kekova cultivar exhibited a sensitive reaction. P. capsici-22 increased the total phenolic compound and H 2 O 2 levels, as well as phenylalanine ammonia-lyase, polyphenol oxidase and peroxidase activities in pepper seedlings. The application of exogenous proline further increased the activities of phenylalanine ammonia-lyase, polyphenol oxidase and peroxidase, as well as the total levels of phenolic compounds and the fresh and dry weights of the plants on the 5 th and 7 th days post treatment. After proline application, the highest catalase activity was found in both cultivars on the 5 th day of the 10 mM proline + P. capsici application. On all days of the experiment, the applications caused a decrease in disease severity, necrosis length and H 2 O 2 levels in both cultivars. In addition, proline decreased the colony growth of P. capsici and the number of zoospores. This finding indicates that enzymes and total phenolic compound levels protect the pepper seedlings against stress-related damage. Moreover, proline has the potential to directly scavenge free radicals and promote enzyme activity in pepper seedlings under P. capsici stress. These results suggest that foliar application of proline is an effective way to improve the stress tolerance of pepper to P. capsici.

Koç E. (2015): Exogenous application of spermidine enhanced tolerance of pepper against Phytophthora capsici stress. Plant Protect. Sci., 51: 127-135.The effect of exogenous spermidine -Spd (0.1 and 1 mM) on the relation between polyaminoxidase (PAO), diaminoxidase (DAO), H 2 O 2 , and malondialdehyde (MDA) in three cultivars of pepper (Capsicum annum L.) exhibiting different tolerance to P. capsici stress: KM-Hot (P. capsici-tolerant), , and CM-334 (P. capsici-highly resistant) was investigated. The 0.1 mM Spd pre-treatment led to an increase in DAO activity on the third day in three pepper cultivars under the stress of P. capsici, 1 mM Spd + P. capsici led to an increase in DAO and PAO activities on the fifth day if compared to P. capsici treatment alone. P. capsici alone caused an increase in the amounts of H 2 O 2 at all times in all cultivars and in the amounts of MDA on the third and fifth days in all cultivars. Conversely; under the stress of P. capsici, pre-application of 0.1 mM Spd at all times in KM-Hot and CM-334 cultivars decreased the amount of MDA and H 2 O 2 and on the first and third days in PM-217 cultivar decreased the amount of MDA and H 2 O 2 . This data indicates that exogenous Spd application before inoculation decreases the plasma membrane injury by decreasing the level of H 2 O 2 and regulating the activities of amine oxidase in both P. capsici-sensitive and P. capsici-resistant cultivars of peppers, so it may increase the tolerance of pepper cultivars against P. capsici.

This study examined the effects of different concentrations of spermine (Spm) and putrescine (Put) elicitors on capsaicin production at different times in cell suspension culture of peper (<em>Capsicum annuum </em>L‘Kahramanmaraş Hat-187’<em>.</em>), raised from pepper seeds. Callus was obtained from hypocotyl explants of pepper seedlings germinated <em>in vitro</em> conditions, and cell suspensions were prepared from calluses. Spm (0.1, 0.2 and 0.4 mg l^-1) and Put (0.1, 0.2 and 0.4 mg l^-1) elicitors were applied on cell suspensions, and control groups free from elicitor treatment were created. The amount of capsaicin in cells was found to be higher in the control groups and samples treated with Spm elicitors when compared to filtrates. The highest increase in the capsaicin amount in cells was determined on day 12 of elicitation with 0.2 mg l^-1Spm application. The highest capsaicin amount passing into the filtrate was determined as 0.1 mg l^-1Spm on day 8. The most effective Put concentration and time on capsaicin amount were found as 0.2 mg l^-1Put on day 12 in both cells and filtrates. The highest total capsaicin was also determined in the 0.2 mg l^-1Spm application on day 12with 312.747 ± 8.70 µg g^-1 of culture. Exogenous treatment of Spm and Put elicitors affected capsaicin accumulation.

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